Herbs & Supplements

Should I take it?

Milk thistle gets its name from the thick white fluid that seeps from the leaves when they are broken. Its long leaves have prominent white veins and sharp spines that can scratch unprotected skin. Purple or pink flowers that grow individually on tall stems bloom in mid-to-late summer. Each milk thistle plant has up to 50 flowers; each flower contains about a hundred seeds. The seeds resemble dandelion seeds, since they are attached to feathery structures that blow in the wind. Thought to have originated in areas around the Mediterranean Sea and possibly regions of India, milk thistle is now found growing wild in most parts of the world with moderate temperatures--including Canada, Europe, and the United States. In cooler climates, it grows as an annual. In warmer areas, it is a biennial bush that can be as tall as 10 feet. Because it spreads rapidly, grows in marginal areas such as vacant lots, and crowds out other plants; milk thistle is often considered to be a weed. Its very strong taproots make it hard to pull up. It may poison cattle and other livestock that eat large amounts of whole plants.

Currently, milk thistle seeds are the part most commonly used in medicine. All the parts that grow above the ground may be used, however, to make extracts. In the past, milk thistle products have been used to stimulate the flow of breast milk in women who were breast-feeding infants. That use is no longer encouraged due to uncertainty about possible effects for the infant. Milk thistle was also a folk remedy for depression. Its leaves, roots, and stems have been eaten as vegetables in some parts of the world, it may be sprouted like alfalfa or beans for salads, and its seeds may be toasted and then boiled into a coffee-type beverage.

Dosage and Administration

Most of the milk thistle products used in human studies were standardized to contain between 70% and 80% of silymarin. Standardization by the manufacturer should assure the same amount of active ingredient in every batch of the commercial preparation. Standardization of herbal products is not required by the U.S. Food and Drug Administration (FDA), so not every product sold in the United States will contain the same amounts of active ingredients.

Standardized commercial preparations of milk thistle are common in Europe. An injectable form of silymarin is also used by European physicians, but it is not available in the United States. In North America, milk thistle is sold most often as an extract, which is a concentrated liquid preparation made by soaking one or more of the chopped or mashed "aerial" parts of milk thistle plants (flowers, leaves, seeds, and stems) in a liquid such as alcohol. This semi-liquid preparation is then strained to filter out the solid parts. It can be packaged as a liquid or dried and made into capsules or tablets. Extracts made only from the seeds of milk thistle are thought not to have estrogen-like effects. The active chemicals in milk thistle do not dissolve very well in water, so making a tea from dried milk thistle is not very useful.

A typical daily dose of milk thistle extract is 200 mg to 420 mg in one, two, or three doses. In clinical studies, the most common length of dosing was 4 weeks to 8 weeks.

Summary

Milk thistle is effective at protecting the liver from toxic substances. In many parts of the world, it is used as an emergency measure to prevent death among individuals who have eaten poisonous mushrooms. It is also taken to prevent or lessen liver damage caused by some medications and industrial chemicals. Milk thistle may have some usefulness for treating liver diseases such as hepatitis and cirrhosis--including alcohol-induced liver damage. Formerly used to promote milk production for women who were breast-feeding, milk thistle has possible mild estrogenic effects that may make it useful for treating certain types of cancer. It is thought to reduce cholesterol to some degree, but more studies are needed to prove its usefulness in the treatment of high cholesterol.

Risks

Due to the estrogen-like effect that may be associated with taking milk thistle, pregnant women and women with hormone-dependent conditions should not take it. Men who have prostate cancer should not take it without the approval of a doctor. Touching milk thistle plants may cause a skin rash.

Side Effects

Side effects from using milk thistle are reported to be mild. They include general gastrointestinal (GI) upset.

Interactions

Milk thistle may interfere with the effects of estrogen replacement therapy and oral contraceptives due to its possible estrogenic effects. The effectiveness of drugs that are broken down by the same enzymes that break down milk thistle may also be affected. Individuals who take prescription medications should ask a doctor or pharmacist about possible interactions before taking milk thistle.

Last Revised October 16, 2007